This invention relates to an outboard motor exhaust tube divider, and particularly to the exhaust system for a two-cycle crankcase compression water cooled V-engine for use in outboard motors.
Such engines, as for example the engine disclosed in U.S. Pat. No. 4,346,676, are normally disposed in the upper unit of an outboard motor and include an exhaust manifold which discharges exhaust gases from a pair of ports downwardly into the usual lower unit and hence through a passage in the propeller to the water. The engines also include a cooling water discharge arrangement for disposing of the cooling water through the lower unit.
An exhaust tube is suitably mounted in the lower unit and provides a single common passage which communicates between the engine exhaust ports and the propeller passage. In some engines of the type under consideration here, the exhaust tube has included an integrally formed rib-like internal housing in its upper end portion. The housing extends inwardly from the tube wall, and furthermore extends from the upper exhaust tube terminus and longitudinally downwardly for a limited distance. The housing forms a channel which opens outwardly through the exhaust tube wall, and which receives a cooling water tube which carries the water from the engine downwardly for discharge.
The above-described construction is such that the upper end of the exhaust tube is partially obstructed by the internal housing.
It has been noted that outboard motors constructed as described above have not performed particularly well at the low end. That is, while the motors have exhibited excellent performance characteristics at high engine speeds, their horsepower has been somewhat below par at low engine speeds, such as about 4000 rpm to 5500 rpm. This has been detrimental to the ability to provide relatively fast acceleration of large boats.
This lack of low end performance has been substantially solved in some prior outboard motors by providing a pair of megaphones which have been mounted to an in-line cylinder engine and which have extended downwardly from the respective manifold discharge ports into the exhaust tube, resulting in fine tuning of the engine. See U.S. Pat. Nos. 3,808,807 and 3,813,880. However, the use of such megaphones in association with the V-type engine described above has not been economically feasible heretofore, due to the obstruction of the exhaust tube by the internal rib-like housing.
It is an object of the present invention to raise the low end performance of an outboard motor engine, even though the exhaust tube upper end is partially obstructed, and in a manner which is simple and economical from a manufacturing standpoint, and without sacrificing high end engine performance.
Broadly in accordance with the various aspects of the invention, divider means is integrated into the upper end of the exhaust tube so that the exhaust discharging from the pair of engine manifold ports remains separated for a portion of its downward travel through the tube. The divider means separates the exhaust tube itself into multiple individual channels. More specifically, a longitudinally extending vertical plate is disposed within the exhaust tube and extends thereacross. The opposed vertical plate edges are anchored to the vertical exhaust tube walls. In the present embodiment, the longitudinally extending cooling tube housing effectively forms part of one of the exhaust tube walls, and with the housing itself forming part of the divider means.